Field of the Invention
The present invention relates to an image processing apparatus and method which are useful in forming a multi-screen using a plurality of image display apparatuses.
Description of the Related Art
Conventionally, when forming a multi-screen by using a plurality of projection type image display apparatuses (to be referred to as image display apparatuses hereinafter), performing luminance correction for an image signal from a region where images from adjacent image display apparatuses overlap implements overall luminance evenness. It is also known that setting an image overlap region with an arbitrary width makes it difficult to visibly recognize even slight differences in display characteristics such as luminance and color tone between image display apparatuses.
In this case, an image display apparatus cannot completely cut off transmitted light when it is of a transmission type or cannot completely cut off reflected light when it is of a reflection type, and hence has a slight luminance even in the black display state. For this reason, in the black display or low gradation display state of a multi-screen arrangement, an image overlap region (to be referred to as an overlap region hereinafter) is higher in luminance than a non-image overlap region (to be referred to a non-overlap region hereinafter), resulting in an uneven luminance. This causes the problem of so-called black floating. Under the circumstances, there has been disclosed a technique which includes independent units for adjusting the luminance of an image overlap region and the luminance of a non-image overlap region and implements luminance evenness in a low gradation display state by independently correcting the luminance level of the non-image overlap region (for example, Japanese Patent Laid-Open No. 2002-268625).
The luminance correction method disclosed in Japanese Patent Laid-Open No. 2002-268625 will be described with reference to FIG. 5. FIG. 5 shows overlap luminances, black correction luminances, and corrected composite luminances for an overlap region and a non-overlap region. In FIG. 5, (5B) indicates the overlap luminance of the overlap region and non-overlap region. In this case, a black correction luminance like that indicated by (5A) in FIG. 5 is used. That is, this corrects the luminances with a correction value of 0 for the overlap region and a significant correction value for the non-overlap region. As a result, a constant composite luminance is obtained as indicated by (5C) in FIG. 5.
However, the overlap accuracy of an image overlap region is not always high as indicated by (5B) in FIG. 5. If the overlap accuracy of an image overlap region is low, the boundary between an overlap region and a non-overlap region shifts to the right as indicated by (5D) in FIG. 5 or shifts to the left as indicated by (5F) in FIG. 5, thus causing a shift phenomenon. When applying a black correction luminance like that indicated by (5A) in FIG. 5 to the former case, the luminance distribution after the correction increases in luminance at the boundary by the shift amount as indicated by (5E) in FIG. 5. When applying a black correction luminance like that indicated by (5A) in FIG. 5 to the latter case, the luminance distribution after the correction decreases in luminance at the boundary by the shift amount as indicated by (5G) in FIG. 5. In either case, the user visibly recognizes a luminance level difference by the shift amount at the boundary between the overlap region and the non-overlap region.
Furthermore, in some case, no luminance edge appears at an end portion of an overlap image, as indicated by (5H) in FIG. 5, due to the low gradation display luminance scattering of an effective image as indicated by (5H) in FIG. 5. In this case, even if an overlap region accurately overlaps a non-overlap region, applying a black correction luminance like that indicated by (5A) in FIG. 5 to the resultant image makes the user visibly recognize a luminance level difference at the boundary in the luminance distribution after correction, as indicated by (5I) in FIG. 5.